This invention relates to an apparatus and method for emptying metallurgical vessels. More particularly, this invention relates to apparatus and method for emptying steelmaking converters containing metal and slag whereby desired separation of slag and metal is effectuated.
When molten metal, particularly steel, is emptied from one vessel into a ladle or any other transport or treatment receiver, a certain amount of slag will generally pass through the tap hole or flow hole near the end of the metal flow. This may result in an undesirable rephosphorization of the steel. Moreover, due to the elevated activity of oxygen in the slag, the metallurgical processing of calmed and semi-calmed steels is made more difficult. Another problem caused by the slag is the risk of critical desulfurization of the steel.
Because of these serious problems, strenuous efforts have been made to avoid slag carryover when metallurgical vessels are emptied. These efforts have resulted in the development of various well known prior art devices including the stop valve, the slide valve and the heavy float. In the heavy float apparatus, a ceramic element floats above the opening of the tap or flow hole and has a cross-section which is larger than that of the flow opening. The ceramic float has a density between that of the metal and slag and functions by obstructing the flow hole after most of the metal has flowed out.
While these prior art devices have been effective in reducing the flow of slag into the ladle or other receiver, they have proved inadequate in diminishing the quantity of slag carried along by the turbulence or vortex which forms above the flow hole. It has been previously suggested that the vortex effect may be reduced by the injection of an agitating gas into the metallic bath through injection nozzles in the immediate vicinity of the flow hole. Unfortunately, the nozzles used to effect this injection are easily susceptible to plugging and therefore require relatively significant quantities of gas during both the pouring and processing phases. This large amount of gas produces the undesirable result of a pronounced cooling of the molten metal. Moreover, the nozzles which contact the molten slag and metal have very limited lifespans relative to the adjacent lining of the crucible. The somewhat disappointing results of the nozzle injection method is probably due to the fact that the gaseous bubbling issuing from the nozzles is not sufficiently distributed in the vortex and therefore does not sufficiently retain the slag.